文档解释
ORA-16574: switchover disallowed when required databases are shut down
Cause: Switchover failed because either the primary database or the designated standby database were shut down.
Action: Ensure that the primary and standby databases are running and that primary database is shipping redo data to the designated standby database. Also ensure that that the designated standby database is applying the redo data received from the primary database.
该错误表明在开始数据库切换过程时发生了错误，这是由于必须在切换之前确保应用于数据库切换操作的数据库当前处于OPEN状态。
